fix(bookkeeping): honor underlag VAT via vat_amount override in categorize flow (#717)

* fix(bookkeeping): honor underlag VAT via vat_amount override in categorize flow

The categorize flow always derived VAT as rate × gross/(1+rate) from the
transaction amount, with no way to use the underlag's actual moms. On e.g.
a restaurant receipt with dricks (no VAT on the tip), the agent could see
the document's correct VAT but the staged booking recomputed the wrong
rate-based amount on every attempt.

- buildMappingResultFromCategory: optional vatAmountOverride replaces the
  rate-derived VAT line ("Ingående/Utgående moms (enligt underlag)"; 0 =
  no VAT line). Rejects negatives, amounts above the 25%-extraction bound,
  and combination with reverse_charge / VAT-less treatments / private.
- gnubok_categorize_transaction: new vat_amount input, threaded into the
  staged preview and persisted in the operation params.
- commitCategorizeTransaction: reads params.vat_amount so the approved
  posting matches the staged preview exactly.
- PATCH /api/pending-operations/[id]: accepts vat_amount (null clears);
  preserves a staged override across category edits while the treatment
  still carries rate-based VAT, drops it when it no longer does.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* review: guard order + agent guidance on vat_amount (PR #717 bots)

- Check treatment compatibility before the 25%-extraction bound so an
  oversized override on reverse_charge reports the actual mistake (the
  treatment), not the amount. Document why the typeof re-check stays:
  commit-time params come from jsonb, so TS types don't hold at runtime.
- vat_amount property description now warns that foreign VAT is never
  deductible as ingående moms and that a 0-moms document should use
  vat_treatment="exempt" rather than vat_amount=0.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* fix(mcp): tools/list payload budget + reject vat_amount 0

core-only failed: the verbose vat_amount descriptions pushed the projected
tools/list payload to 36,051 tokens (ceiling 36,000; main is at 35,862).
Per the guard's own guidance, trim descriptions instead of bumping:
now 35,943.

Folds in the Swedish review's round-2 point while trimming: vat_amount 0
is now rejected with a pointer to vat_treatment "exempt". A 0-moms
document is an exempt supply — "exempt" produces the identical expense
booking and the correct income account (3004), so 0 had no use case and
only created a silent momsdeklaration misclassification path. Schema
declares exclusiveMinimum: 0.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* fix(bookkeeping): use roundOre for vat_amount math (antipattern ratchet)

Second core-only failure: the naive-ore-round ratchet caught the new
Math.round(x*100)/100 lines (662 > baseline 661). Switch the override
path to roundOre from lib/money — including the pre-existing computed-VAT
line this PR touched — and ratchet the baseline down (659, raw-route-auth
168 locked in from main-side fixes).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

lib/pending-operations/commit.ts

@@ -256,6 +256,13 @@ async function commitCategorizeTransaction(
     typeof params.notes === 'string' && params.notes.trim().length > 0
       ? (params.notes as string)
       : undefined
+  // The underlag's actual VAT, staged when the document's moms differs from
+  // rate × belopp (e.g. dricks). Threaded into the mapping builder so the
+  // approved posting matches the staged preview exactly.
+  const vatAmount =
+    typeof params.vat_amount === 'number' && Number.isFinite(params.vat_amount)
+      ? params.vat_amount
+      : undefined
 
   const { data: transaction, error: fetchError } = await supabase
     .from('transactions').select('*').eq('id', txId).eq('company_id', companyId).single()
@@ -276,7 +283,7 @@ async function commitCategorizeTransaction(
   const fiscalYearStartMonth = settings?.fiscal_year_start_month ?? 1
 
   const mappingResult = buildMappingResultFromCategory(
-    category, transaction as Transaction, isBusiness, entityType, vatTreatment
+    category, transaction as Transaction, isBusiness, entityType, vatTreatment, vatAmount
   )
 
   if (!mappingResult.debit_account || !mappingResult.credit_account) {